/Engine/Source/Editor/BlueprintGraph/Classes/EdGraphSchema_K2.h
Create sub menu that shows all possible variables that can be used to replace the existing variable reference
static void GetReplaceVariableMenu ( [UToolMenu](API\Developer\ToolMenus\UToolMenu) * Menu, class [UK2Node_Variable](API\Editor\BlueprintGraph\UK2Node_Variable) * Variable, [UBlueprint](API\Runtime\Engine\Engine\UBlueprint) * OwnerBlueprint, bool bReplaceExistingVariable )